It is well established that the exhaustion of combustion gases through a chimney using natural draft is energy wasteful. Moreover, it promotes a turbulent flow of gases, in the combustion appliance, with sooting and rapid, premature corrosion resulting therefrom.
Many proposals have heretofore been advanced for power vents. In accordance with certain proposals, a blower located indoors is used, and draft control is provided by permitting the entry of ambient room air to the blower. This is energy wasteful, and blower temperatures tend to be high, leading to rapid corrosion of the blower and motor failure.
In accordance with other proposals as exemplified U.S. Pat. Nos. 4,757,802 (GUZOREK) and 4,424,792 (SHIMEK et al), the blower unit locates outdoors, and outside air is used for draft control, tending to overcome the foregoing problems. However, there are other problems associated with these vent structures, particularly in cold, northern climates, due to condensation and icing in the blower unit and outlet thereto, and in the motor requiring an auxiliary heating circuit or other provisions to overcome bearing drag. Additionally, in one proposal, in order to provide a compact outdoor unit, the shaft of the blower unit is arranged in axial alignment with the vent tube, and the exhaust is downwardly directed, whereby problems of exhaust recirculating into the fresh air entry duct may be experienced. Moreover, installation and maintenance of a power vent wherein operative components are located outdoors is increased in comparison to where such components are located indoors.
It has recently been observed that buildings may have a pronounced thermal updraft associated therewith. Where a hooded, downwardly opening aperture is provided adjacent a building wall, the hood acts as a wind scoop, and a current of cold outside air may flow through a vent tube. Flat valves are well known, but may not be permitted for use in chimney vents by many building codes.